Developing applications that use complex platforms for functionalities such as authentication and messaging is hard. Model-driven engineering promises to help, but transformation systems are themselves hard to produce. We contribute a new approach using constraint-based synthesis of partial code frameworks that developers complete by hand without the need for hand-coded transformation systems. Rather, synthesis is driven by formal, partial specifications of target platforms and application architectures, and by design (code) fragments encoding application-specific platform usage patterns. We present results of an early evaluation using the case study method to test hypotheses of feasibility and potential industrial utility, using a laboratory model of a nationwide health information network as a subject system.